Well there is little i could do for you, sorry, in the UK there is a very helpful little magazine called computer activ, ever heard of it? It gives you a step by step guide of how to fix problems like that.
For the first point: if your router has DHCP activated, go and check if the DHCP client service is running on your machine. Furthermore check the settings of your network adapter.
Is your cable okay? If you can see a damaged rubber or even a damaged braid, then use another cable.
Do others in your house/flat have internet access?
Just in case you use DHCP try the following:
Press your 'Start' button, then 'Run' and type services.msc. There should pop up a list of names, where you have to look for DHCP client. If it doesn't run, start it. This is the part of your desktop.
For the router: I don't know the exat IP adresses of your network. Try typing one of the following IP adresses in your browser:
192.168.0.1
192.168.1.1
192.168.2.1
Or if you know the IP of the router, type it in your browser. Enter the settings menu of your router and look for a point like 'LAN IP setup' or so. It depends on your router model. Have a look at the manual, if you don't know where to look exactly. The settings there should be self-explanatory.
If your router isn't used as DHCP server, well then give your desktop an adequate IP adress. Look within the settings of the other PCs if they are connected via cable, too. WLAN uses another network adapter and therefore some other IP range.
Well... if this doesn't help, provide me with more information.
from this you can see if your PC's DHCP client is enabled, and what IP address your PC has.
your IP address should read 192.168.X.XXX if you have a generic Router and the DHCP is functioning correctly. if it says 169.254.1.XXX then the DHCP client could not acquire an address from your router.
usually single PC internet problems are caused by something at that PC, either with the cable or the Network card/driver/settings. use the same IPconfig Command on another PC on the network and see if that pc settings are different from the non connecting PC.
you can try an uninstall/reinstall of your network drivers from the control panel to reset the driver and the settings.